No. 750w is recommended.
Also, get a 4gb stick rather than dual channeling 2 x 2gb stick. It's better if you can go 8gb though.
750W is recommended for SLI on those cards. Yes, it is better to go with 1 4gb stick so you can upgrade to 8gb later. On a gaming computer 4gb will be close to used up and with new games coming out it is worth the extra $20-$30 on 8gb of ram.
Where are you buying from?